Inexpensive pair of bookshelf speakers.

What aspects of sound reproduction are most important to you? Tough to make a good recommendation without that info, but the Silverline Minuets are good all around speaker. Best of luck.

I heard the Paradigm Studio 20's and was very impressed used around 400-600 for v3 to v4

I like the KEF Q300 bookshelf speakers in that price range you mention. They also work well with tube power. I've used these speakers with Jolida amplification.

Good point Soix,
Musical speakers desinged with the goal of reproducing music at the highest level.

Open 3 dimensional soundstage, spot on imaging, taut bass, uncolored with excellent midrange for the best possible reproduction of the type of music I listen to.

I guess I'm looking for the holy grail in terms of musicality and affordability.

I once owned the Totem Model 1 and I regret parting ways with them. Looking for something similar in sound but at a more affordable price.

Maybe too much to ask?

It is a lot to ask, Kiko65, but lots of fun bargain-hunting in this price range. Much more fun, I think, trying to "get lucky" with a $600 pair of speakers than a $6000 pair of speakers (where your expectations can run so high).

From my own personal experience - and I've not owned everything - I keep thinking a pair of the Sonus Faber Concertos, 2nd version (the non-biwire ones). They can rock when they need to, but when you need them to put Diana Krall in the room with you they can pull it off. They can sound pretty, which you will need if you want to enjoy Krall, Norah Jones, Allison Krauss, etc. And when you need to crank "D'yer Mak'er", they won't fall down. That's the only issue at this price range...many speakers will do one or the other well, but not both. The SF Concertos play well with tubes, they won't overload your room, and when you need resolution at lower volumes they can do it. They were $2K new, but I've seen them for around $600 used, albeit maybe not flawless. But on the used market, it's a ton of speaker for $600 and gorgeous if you can find them in the real Italian walnut.